demo.java

这是《Java 2 简明教程(第2版)》一书配套的源代码。

class RunDemo
{
  private String userName,password;

  RunDemo()
  {
    System.out.println("All is null!");
  }
  
  RunDemo(String name)
  {
    userName=name;
  }

  RunDemo(String name, String pwd)
  {
    this(name);
    password=pwd;
    check();
  }
 
  void check()
 {
   String s=null;
    if(userName!=null)
      s="userName:"+userName;
    else                                        
      s="please input your password!";
    if(password!="ThisWord")
      s=s+"   invaid!";
    else
      s=s+"  password:********";
    System.out.println(s);
  }
}

public class Demo
{
   public static void main(String args[])
    {
      new RunDemo();
      new RunDemo("Bill");
      new RunDemo(null,"Bill");
      new RunDemo("Bill","ThisWord");
    }
}